Decanting liquids containing flocculated material



Dec. 17, 1957 (j, BQUNIN 2,816,661 Y DECANTING LIQUIDS CONTAINING FLOCCULATED MATERIAL Filed May 19, 1954 2 Sheets-Sheet 1 IN VEN TOR.

CHBounz/Ib BY C. BOUNIN Dec. 17, 1957 DECANTING LIQUIDS CONTAINING FLOCCULATED MATERIAL Y 2 Sheets-Sheet 2 Filed May 19, 1954 INVENTOR.

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United States Patent DECANTING LIQUIDS CONTAINING FLOCCULATEID MATERIAL Claude Bounin, Paris, France Application May 19, 1954, Serial No. 430,947

Claims priority, application France November 25, 1953 4 Claims. (Cl. 210-83) This invention relates to an improved method of and apparatus for decantation.

The present invention, briefly described, comprises the feature that solid surfaces are moved in liquid, in the course of decantation at a speed below the speed at which eddy currents would be set up in the liquid and produce agitation, the mean plane of said surfaces making an acute angle with the direction of motion of said surfaces.

In my co-pending patentapplication No. 362,767, I have described a method of decanting liquids containing material in suspension which consists in passing through the flocculated material in the course of decantation a device comprising a screen or grid consisting of fine wires moving at a low speed, that is, not exceeding twenty centimeters per second, wherein the surfaces of the grids or screens or planes tangential to the said surfaces, form acute angles with the direction of displacement.

In a general way there can be distinguished, in a decantation vat, with or without the device according to the invention described in my said co-pending application, three zones:

(a) the zone of decantation properly so called, in which gravity has a kinetic action upon the descent of the particles in the liquid;

(b) a zone of compression, in which gravity determines dynamic interactions between the particles and the liquid;

(c) a zone of settling, in which the particles exert upon one another an action which is primarily static or in other words a zone wherein solid particles exert a compressive force on one another.

More recently I have recognised that in the compression zone, which follows the decantation zone properly so called, and/ or in the settling zone which follows the compression zone, it is desirable to replace the grids or screens by solid surfaces, also making an acute angle with the direction of displacement.

These solid surfaces are preferably plane, but they may be curved, always on the condition that planes tangential thereto make an acute angle with the direction of displacement. In particular, these solid surfaces may be constituted by horizontal wings forming an acute angle with the direction of displacement, arranged downward from above upon a vertical pivot, with a space intervening between them, to afford free passage for the suspension to be decanted. They may be arranged like a staircase. The one below another along the vertical axis.

9 In all cases the displacement will occur at a low speed, the speeds being equal, but admitting of being slightly different in different zones.

The process according to the present invention, which consists therefore in utilising a device comprising solid surfaces moving at a low speed in the zone of compression and/or in the settling zone, may be applied either by utilising, in the zone of decantation, grids or screens in accordance with my said co-pending application, or else by utilising in this decantation zone solid surfaces under the conditions indicated in the present specification,

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since I have found that in this latter case the liberation of the water retained by the agglomerates is effected satisfactorily, always on the condition of maintaining low speeds.

Therefore, the invention provides a method of accelerating the rate of solids-liquid separation in a suspension of solids in liquid of the type in which the solids have such a natural or artificially induced weight as to be capable of eventually settling by gravity in that the solid particles can overcome the viscosity of the suspending liquid. As indicated previously when such a suspension is confined, there is established within the vat, tank or decanter a plurality of superposed zones. The clarified liquid zone is uppermost or at the top, beneath this zone is the zone of decantation or what can also be termed the zone of independent subsidence where solid particles or flocks settle independently, the settling rate being dependant upon the size and density of the particle or floc. The next subjacent zone is a zone of compression or what is also termed a zone of collective subsidence in which the settling rate decreases with the increasing concentration of solids. The settling rate is influenced by particle or floc interference. The next lower zone is a zone of settling or what can be termed a zone of cornpressive subsidence where fiocs and/or particles are in intimate contact and the subsidence is due to compression, that is the pressure of particles or does upon one another.

The invention effects the acceleration of the rate of separation by applying in at least two of the zones below the clarified liquid a downwardly directed deflection to solid and liquid particles over a vertical cross-sectional area in the two zones that is large in relation to the total surface area of suspension being treated with the deflection being applied horizontally at an acute angle and at a selected speed below twenty centimeters per second that will prevent the occurrence of eddy currents that would cause hydrodynamic disturbances in the decantation zone, the deflection being applied without exerting direct horizontal compressive forces acting perpendicular to the direction of displacement in the decantation and compression zones so as to downwardly deflect solid particles and facilitate liquid separation.

Specifically, the invention provides a method of accelerating the rate of solids-liquid separation by horizontally displacing through at least partof two adjacent zones of a confined suspension of the above type solid surfaces inclined at an acute angle to the direction of displacement and which surfaces are maintained at substantially the same angle during such horizontal displacement and which surfaces are maintained at substantially the same angle during such horizontal displacement, are thin in relation to their surface area and have a total surface area in the two zones that is large in relation to the surface area of the suspension being treated.

The invention is illustrated by way of example in the accompanying drawings, in which:

Figure 1 represents in axial section a vat provided with a decantation device according to the present invention;

Figure 1B is a fragmentary cross-section of the arrangement of Figure 1, illustrating the blades as curved;

Figure 2 is a plan view of the same device;

Figure 3 is an axial section showing another embodiment of the invention;

Figure 4 is a plan view of the device shown in Figure 3;

Figure 5 is a cross section of a vat provided with a third form of construction of the invention;

Figure 6 shows the same vat in longitudinal section; and

Figure 7 illustrates on a larger scale a detail of the device shown in Figures 5 and 6.

In these examples, which are very diagrammatically illustrated, some of the examples from my co-pending application are intentionally included, in order to bring out clearly the differences between my said co-pending application and the present: invention.

Figures 1, 1B and 2 show a cylindrical vat of small diameter, for instance of a diameter of the order of a few metres. Dot-and-dash lines are employed to indicate the levels that separate the zone of decantation D in. the upper part and the settling zone T in the lower part from the zone of compression C between these two zones. It will be understood that these are mean zones, and that there is not really any clearly marked surface bounding the various zones, the passage from one to the other being practically continuous.

Around a rotatable shaft 8-, which coincides with the geometrical axis of the vat 1, are arranged six sets of deflection applying means. Thus in the decantation, compression and settling zones are blades or wings 9 the direction of which is in general horizontal. As shown in Figure 1B the blades are curved and the planes tangen tial thereto make acute angles with the direction of displacement. In the drawings the axes of the wings have been shown in the same plane, but it is to be quite understood that this arrangement is by no means necessary. A helical arrangement might for example be adopted.

By means of the spindle 8 a very slow rotation is imposed on the assembly, the mean speed being of the order of a few centimeters per second, so as not to create any hydrodynamic eddies.

The suspension is fed into the vat or decanter 1 in a conventional manner such as through the inlet denoted diagrammatically at 50, the clarified liquid is withdrawn as is conventional through outlet means such as at 51 while settled solids are withdrawn from the bottom through outlet means such as at 52. In Figure 1 the arrangement of blades presenting the solid surfaces is illustrated, there being six radially arranged sets of blades at a plurality of vertically spaced levels which present a total surface area effective to establish deflection, that is very large in relation to the surface area of suspension within the vat or decanter 1. All of the blades as indicated in Figure 1B are supported at substantially the same acute angle and with the same pitch to the horizontal, so that during the very slow horizontal displacement the solid deflecting surfaces always exert a downwardly directed component of force on solids and liquids. There is no direct upward compressive forces exerted during horizontal displacement. The speed of movement is a selected rate of movement that is so slow, a few centimeters per second, that no hydrodynamic eddies are established.

In Figures 3 and 4, the same cylindrical vat is shown provided with surfaces inclined at a much greater angle to the direction of displacement. In the lower part only a single surface has been shown, which consists of a sheet-iron plate 11, in which transverse rectangular apertures have been cut, thereby constituting a different method of obtaining, between the apertures 12, wings analogous to those illustrated in Figure l. The decanter 1' in Figure 3 is fed with suspension in a manner similar to the arrangement of Figure l and the different zones or levels have been diagrammatically indicated by dot and dash lines also as shown in Figure 1. The solid surfaces or blades formed by the portions of the blade 11 on each side of the apertures 12 have such an extent in this modification as to occupy part of two adjacent levels within the suspension.

This is consistent with what has been stated previously in that if the primary result desired is to operate the decanter as a thickener the solid deflecting surfaces will be in the zone of compression and in the settling zone. if the decanter is to be operated as a clarifier the solid deflecting surfaces will be in the compression zone and in the decantation zone.

lnother words, the deflection will be applied in at least two adjacent levels in a confined suspension. In Figure l the deflection is applied in such number of vertically spaced levels as will establish the deflection in all the zones within the decanter in which the solid particles are present.

In the upper part a single grid 10 has been provided. As Figure 3 shows, the two surfaces It) and 11 make acute angles with the direction of displacement, which is indicated in Figure 4 by an arrow, so that a component of the light shock which the particles receive on meeting the moving surfaces has the effect of giving these particles an impulse clearly directed towards the bottom of the vat.

It would of course be possible and advantageous to mul tiply the number of surfaces such as 10 and 11, spacing them apart angularly and distributing them around the shaft 8, either at the same height or at different heights. The blade 11 is mounted on a short radial arm that is secured to shaft 8 and the grid 10 is mounted on another short radial arm 61 that is likewise secured to shaft 8'.

In the example illustrated in Figures 5, 6 and 7, the vat 29 is of rectangular horizontal cross section, and terminates in a tapered bottom. The vat is fed with suspension at one end through inlet feed means denoted at 53 and clarified liquid is withdrawn through outlet means denoted at 54. In this example four orientable surfaces 29, 21, 22 and 23 are shown. The surfaces 20 and 21 are grated frames analogous to those that have been described in the preceding examples. The surfaces 22 and 23 are plane surfaces, which may either be solid, or else out out into blades as described in the preceding example.

These four surfaces are pivoted upon vertical arms 24 and 25 in such a way as to be rotatable about horizontal axes.

The arms 24 and 25 are rigid with a horizontal frame 26, which is carried by wheels 36. The wheels 36 move along rails 27 and 28 arranged one on each side of the decanter. The frame 26 supports a driving box 40, which contains the mechanism enabling the angular position of the surfaces to be reversed.

This mechanism comprises two gear wheels 35, on rotatable shaft 34. The wheels 35 mesh with a rack 32, which is freely slidable in the frame 26, by any convenient guiding means.

The rack 32 carries at each end a buffer 33, which may if desired be mounted resiliently, and which is designed to strike against stationary abutments 30, 31 which are fixed in relation to the vat. Each of the horizontal pivotal shafts of the surfaces 20, 21, 22 and 23 carries a fly-wheel 38, which is connected by a connecting-rod or by a chain 37 to the gear wheels 35. The various wheels 38, corresponding severally to the surfaces 20, 21, 22 and 23, are connected with one another by connecting-rods or chains 39.

As will be seen from Figures 6 and 7, the surfaces 20, 21, 22 and 23 make acute angles with the direction of displacement, which is assumed in these figures to be from left to right. When the box 40, the frame 26 and the surfaces that it supports reach the end of their travel to the extreme right of Figure 6, the buffer 33 strikes against the fixed abutment 31. The rack 32 then undergoes a displacement towards the left relative to the box 40. This turns the gear wheels 35 through a certain angle, the value of which is limited by any suitable system of stops, in such a way that the rotation of the wheels 38 brings the surfaces 20, 21, 22 and 23 into a position symmetrically opposite to that illustrated. The carriage then moves towards the left, until the left-hand buffer 33 strikes against the fixed stop 30, which has the result of again reversing the inclination of the surfaces 20 to 23.

The means for driving the carriage and the means for reversing. the direction of travel have not been illustrated, since these are common technical devices, and can be carried out in a great variety of ways, the reversing means being of course synchronised with the displacements of the rack 32.

The numeral 41 denotes a device by means of which the rack can be locked, if desired, by interposing an arresting catch between the teeth of the rack.

As seen in the preceding examples, the speed of displacement will be a few centimeters per second.

In the foregoing examples, the scrapers that serve for the evacuation of the sludge at the bottoms of the vats, since they are well known and are in general use, have not been shown. It will be obvious, however, that these scrapers must not be confused with the surfaces or wings of the device according to the invention.

It is to be pointed out that illustrated form of decantation apparatus is only exemplarly since any conventional type decanter can be utilized in practicing my invention by associating therewith one or more diametrical series of blades or vanes and rotating the same at very low speeds. As mentioned in my prior filed application Serial 362,767, filed June 19, 1953, the peripheral speed of an apparatus utilizing grids inclined at an acute angle to the horizontal will approximate 20 cms. per second. It is believed clear that where, as in this example, the grids are eliminated and the rotating blades are solid surfaces, the speed of movement will be less and amount to only a few cms. a second.

In the decantation of a dispersion of solids in liquid in accordance with this invention, the displacement or movement of the solid bodies at a speed of a few cms. per second is so slow that there is no agitation or disturbance of the material in the vat and thus no eddy currents are formed. The movement of the solid bodies deflects the portions of solid and liquid in advance of each body and constrains the same to flow downwardly across the lower face or trailing edge of each blade. This action accelerates the rate of settling of the solids and since the liquid phase is lighter than the solid phase the liquid will tend to flow upwardly around the trailing edge of each blade whereby this action establishes what can be termed a separating zone at the trailing edge of each blade.

It is clear that the blades, when arranged in superposed series of blades will be vertically displaced a distance suflicient to permit the slow movement of the series of blades through the dispersion and will further permit any liquid phase that is not being impinged upon by the advancing blades to pass between the superposed blades.

It is clear that this invention can be practiced with any type decantation vat regardless of whether the outlet at the bottom is centrally disposed or is at the periphery of the decantation chamber. The essentialities of the invention comprise the combination of moving solid bodies through the dispersion at a speed of a few cms. per second while simultaneously and very slowly deflecting the solids and liquids impinged upon by the bodies to flow downwardly and rearwardly as regards the direction of movement of the bodies at an acute angle to that direction of movement to facilitate settling of the solids and separation of the liquids.

Specifically the invention incorporates an arrangement of blades that are inclined at an acute angle to the horizontal. In Figures 3 to 7 these blades are flat planar surfaced blades whereas in Figures 1 and 2 the blades are curved with the concave side being the active face that deflects the material in the vat, or in other words the blades have an air-foil cross-section.

It is to be further pointed out that the present method contemplates horizontal moving blades disposed at an acute angle to the direction of movement in vertically displaced planes in the decantation apparatus and which blades exert a deflecting action in the settling zone, the zone of compression wherein gravity determines dynamic interactions between solids and liquids and the uppermost zone of decantation in which gravity has a kinetic action upon the descent of the solids through the liquid.

What I claim is: s

l. A method of accelerating the rate of solids-liquid separation comprising continuously feeding and confining a suspension of solids in liquid of the type in which the solids have such a natural or an artificially induced weight as to be capable of eventually settling by gravity in that the solid particles can overcome the viscosity of the suspending liquid to establish at least three superposed zones comprising a lower settling zone wherein solids exert a compressive force on one another, a zone of compression wherein the particles of solids settle under conditions determined by gravity but are close to one another and an upper decantation zone wherein the solids usually receive kinetic energy to descend due to the force of gravity and in which the solid particles are spatially separated from one another, withdrawing separated liquid from above the decantation zone and in at least two adjacent zones applying a downwardly directed deflection to solid and liquid particles over a vertical cross sectional area in the said two zones that is large in relation to the total surface area of suspension with the deflection being applied by horizontal displacement thereof through the suspension at an acute angle and at a selected speed below 20 centimeters per second that will prevent the occurrence of eddy currents and cause hydrodynamic disturbance in the decantation zone and applying the deflection without exerting direct horizontal compressive forces in the decantation and compression zones whereby the deflection functions in the said at least two zones to downwardly deflect solid particles and facilitate liquid separation.

2. A method of accelerating the rate of solids-liquid separation comprising continuously feeding and confining a suspension of solids in liquid of the type in which the solids have such a natural or an artificially induced weight as to be capable of eventually settling by gravity in that the solid particles can overcome the viscosity of the suspending liquid to establish at least three superposed zones comprising a lower settling zone wherein solids exert a compressive force on one another, a zone of compression wherein the particles of solids settle under condi tions determined by gravity but are close to one another and an upper decantation zone wherein the solids usually receive kinetic energy to descend due to the force of gravity and in which solid particles are spatially separated from one another, withdrawing settled solids from below the settling zone, withdrawing separated liquid from above the decantation zone and in different vertically spaced levels of the suspension including at least one level in each of two adjacent zones applying and horizontally displacinga deflection to solid and liquid particles over a vertical cross sectional area in the said two zones that is large in relation to the total surface area of suspension with the deflection being applied at an acute angle to the horizontal and at a selected speed below twenty centimeters per second that will prevent the occurrence of eddy currents and cause hydrodynamic disturbance in the decantation zone, and applying the deflection without exerting direct horizontal compressive forces acting perpendicular to the direction of displacement in the decantation and compression zones whereby the deflection functions in the said at least two zones to downwardly deflect solid particles and facilitate liquid separatron.

3. A method of accelerating the rate and degree of solids-liquid separation comprising confining a body of suspension of solids and liquid of the type in which the solids are capable of eventually settling by gravity in that the solid particles can overcome the viscosity of the suspending liquid to establish at least three superposed zones comprising a lower settling zone wherein solids exert a compressive force on one another, a zone of compression wherein the particles of solids settle under conditions determined by gravity but are close to one another and an upper decantation zone wherein the solids usually receive kinetic energy to descend due to the force 7 of gravity and in which solid particles are spatially separated from one another, and in difierent vertically spaced levels in each of said zones over a substantial total vertical cross sectional area of the suspension that is large in relation to the surface area of the confined suspension applying and horizontally displacing a downwardly directed deflection to solid and liquid particles in each spaced level at an acute angle to the horizontal in the same direction in each level at a selected speed of movement below twenty centimeters per second such as to prevent the formation of eddy currents that would cause hydro-dynamic disturbances while maintaining the application of deflection without exerting any undue horizontally directed compressive forces acting perpendicular to the direction of displacement or any undue directly applied upwardly directed compressive forces during displacement so that the rate of solids settling is accelerated and the rate of rise of liquid is simultaneously accelerated.

4. A method of accelerating the rate of solids-liquid separation comprising continuously feeding and confining a suspension of solids in liquid of the type in which the solids have such a natural or an artificially induced weight as to be capable of eventually settling by gravity in that the solid particles can overcome the viscosity of the suspending liquid, to establish at least three superposed zones comprising a lower settling zone wherein solids exert a compressive force on one another, a zone of compression wherein the particles of solids settle under conditions determined by gravity but are close to one another and an upper decantation zone wherein the solids usually receive kinetic energy to descend due to the force of gravity and in which solid particles are spatially separated from one another, withdrawing settled solids from below the settling zone, withdrawing separated liquid from above the decantation zone, supporting a plurality of thin vertically spaced imperforate blades within and horizontally displacing the same through the suspension in at least two of said zones while maintaining the blades inclined at an acute angle to' the direction of displacement during such horizontal displacement and effecting horizontal displacement at a selected speed sufficiently below twenty centimeters per second to prevent the formation of eddy currents and cause hydrodynamic disturbances in the decantation zone, to apply a horizontally moving downwardly directed deflection in the said at least two zones to accelerate the settling of solid particles and facilitate rise of liquid.

References Cited in the file of this patent UNITED STATES PATENTS 785,522 Robinson Mar. 21, 1905 1,605,596 Langelier Nov. 2, 1926 1,842,938 Hancock Jan. 26, 1932 1,851,684 Priiss Mar. 29, 1932 1,912,019 Steindorf Nov. 30, 1933 2,000,418 Ruth May 7, 1935 2,101,081 Lund Dec. 7, 1937 2,301,461 Schnetz Nov. 10, 1942 2,361,283 Good Oct. 28, 1944 2,392,731 Fox -2 Jan. 8, 1946 2,499,816 Carter Mar. 7, 1950 2,596,082 Stuart May 6, 1952 2,610,836 Clarke Sept. 16, 1952 

